Villard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Villard clear sky chart from 2005-11-06 to 2024-11-30.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	12% 8% 3 8% 5% 5% 5% 4 6% 8% 37%	101872
	Night	11% 9% 3 8% 5% 5% 5% 4 6% 7% 38%	97828
Transparency	Day	44% 5% 14% 26% 11% 1	105463
	Night	44% 4 13% 25% 12% 1	102380
Seeing	Day	15% 10% 31% 27% 14% 3	16142
	Night	15% 9% 33% 32% 11% 1	26063

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	9% 16% 4 14% 11% 8% 6% 3 5% 5% 18%	2218
	11th to 20th	Day	5% 9% 6% 15% 7% 8% 10% 7% 8% 6% 20%	2451
	21st to end	Day	5% 14% 10% 17% 8% 7% 5% 5% 5% 6% 17%	3135
February	1st to 10th	Day	8% 12% 5% 11% 6% 6% 6% 4 6% 10% 28%	1710
	11th to 20th	Day	6% 11% 4 9% 9% 7% 6% 5% 7% 8% 30%	1664
	21st to end	Day	8% 13% 4 11% 8% 7% 5% 4 7% 8% 25%	1465
March	1st to 10th	Day	12% 12% 4 10% 6% 6% 4 4 5% 6% 34%	3377
	11th to 20th	Day	8% 11% 4 8% 5% 4 5% 3 5% 9% 38%	3480
	21st to end	Day	19% 13% 5% 13% 8% 5% 4 3 5% 6% 21%	3814
April	1st to 10th	Day	16% 10% 3 6% 5% 4 4 4 5% 8% 36%	2228
	11th to 20th	Day	17% 13% 4 7% 4 4 3 3 6% 6% 33%	2399
	21st to end	Day	23% 11% 3 6% 4 4 4 4 4 6% 32%	2470
May	1st to 10th	Day	16% 7% 3 6% 4 4 4 4 5% 7% 39%	4110
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 5% 8% 43%	4399
	21st to end	Day	16% 6% 3 6% 5% 4 5% 4 7% 9% 35%	4824
June	1st to 10th	Day	11% 5% 2 6% 4 5% 4 4 6% 9% 43%	2806
	11th to 20th	Day	14% 6% 3 7% 5% 3 4 4 7% 7% 38%	2850
	21st to end	Day	10% 5% 2 5% 4 5% 5% 5% 7% 10% 42%	2850
July	1st to 10th	Day	9% 5% 2 5% 4 5% 6% 5% 8% 11% 39%	4750
	11th to 20th	Day	4 3 1 4 3 3 4 4 6% 9% 58%	4729
	21st to end	Day	5% 4 2 6% 5% 4 5% 4 7% 9% 49%	4596
August	1st to 10th	Day	12% 5% 2 5% 3 4 5% 4 6% 9% 44%	4104
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 10% 41%	4041
	21st to end	Day	10% 6% 2 6% 4 4 4 3 5% 8% 47%	4500
September	1st to 10th	Day	10% 5% 1 5% 3 3 5% 3 6% 7% 52%	2280
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 5% 7% 47%	2132
	21st to end	Day	15% 6% 2 5% 3 3 4 3 5% 7% 48%	2076
October	1st to 10th	Day	17% 8% 2 5% 4 3 4 3 5% 7% 41%	1900
	11th to 20th	Day	15% 11% 3 6% 3 3 4 3 5% 6% 41%	1900
	21st to end	Day	17% 10% 4 7% 4 4 4 3 4 5% 37%	2035
November	1st to 10th	Day	15% 13% 3 8% 4 4 3 4 6% 6% 34%	1629
	11th to 20th	Day	10% 13% 5% 14% 7% 6% 5% 3 5% 6% 27%	1600
	21st to end	Day	12% 11% 5% 12% 6% 5% 5% 3 5% 8% 29%	1597
December	1st to 10th	Day	8% 12% 6% 13% 9% 6% 7% 5% 5% 6% 24%	1520
	11th to 20th	Day	10% 13% 6% 12% 7% 6% 5% 4 5% 7% 25%	1791
	21st to end	Day	20% 14% 5% 14% 8% 3 4 2 4 6% 20%	2442
January	1st to 10th	Night	8% 11% 5% 15% 10% 6% 6% 4 6% 6% 24%	4737
	11th to 20th	Night	5% 11% 4 13% 9% 9% 12% 6% 7% 6% 17%	4516
	21st to end	Night	6% 16% 11% 14% 5% 5% 5% 4 6% 6% 22%	4532
February	1st to 10th	Night	5% 11% 5% 9% 7% 6% 5% 5% 7% 8% 32%	2470
	11th to 20th	Night	5% 10% 4 8% 5% 5% 6% 5% 7% 7% 37%	2403
	21st to end	Night	10% 11% 4 8% 5% 6% 5% 4 6% 8% 33%	2007
March	1st to 10th	Night	8% 7% 3 8% 5% 4 4 5% 6% 7% 44%	3479
	11th to 20th	Night	8% 9% 3 8% 6% 4 5% 4 6% 8% 39%	3480
	21st to end	Night	22% 13% 4 10% 6% 3 3 3 4 5% 27%	3817
April	1st to 10th	Night	15% 9% 3 6% 4 4 4 3 5% 7% 40%	1952
	11th to 20th	Night	16% 11% 4 8% 4 4 4 3 5% 6% 36%	1728
	21st to end	Night	17% 10% 3 7% 4 3 5% 3 5% 5% 38%	1710
May	1st to 10th	Night	16% 8% 3 6% 4 4 3 3 4 7% 44%	2792
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 3 5% 6% 46%	2506
	21st to end	Night	16% 8% 2 6% 4 4 4 4 5% 7% 40%	2743
June	1st to 10th	Night	10% 5% 1 4 4 5% 3 4 5% 9% 50%	1370
	11th to 20th	Night	9% 5% 3 5% 4 4 4 4 7% 9% 46%	1330
	21st to end	Night	8% 5% 2 4 4 3 4 3 7% 8% 53%	1330
July	1st to 10th	Night	9% 5% 2 5% 4 5% 6% 4 6% 10% 43%	2220
	11th to 20th	Night	3 3 1 4 3 3 4 3 5% 7% 65%	2237
	21st to end	Night	5% 3 1 5% 3 4 4 4 7% 9% 54%	2964
August	1st to 10th	Night	9% 7% 2 5% 3 4 4 3 6% 7% 51%	2836
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 5% 8% 50%	2798
	21st to end	Night	8% 5% 2 5% 3 3 4 4 5% 9% 52%	3166
September	1st to 10th	Night	9% 4 1 4 3 3 3 2 6% 8% 57%	1900
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 5% 6% 53%	2046
	21st to end	Night	11% 6% 2 5% 3 3 3 2 4 6% 53%	2090
October	1st to 10th	Night	13% 7% 2 6% 4 3 4 3 5% 7% 46%	2275
	11th to 20th	Night	13% 9% 2 6% 5% 3 5% 3 5% 7% 43%	2280
	21st to end	Night	15% 11% 4 8% 3 3 4 3 5% 7% 36%	2560
November	1st to 10th	Night	11% 9% 3 7% 5% 4 5% 4 7% 7% 39%	2669
	11th to 20th	Night	11% 12% 4 12% 6% 4 4 4 5% 6% 33%	2800
	21st to end	Night	10% 10% 4 9% 6% 5% 4 3 6% 6% 37%	2799
December	1st to 10th	Night	8% 13% 5% 11% 8% 5% 5% 3 7% 7% 28%	2660
	11th to 20th	Night	10% 12% 4 12% 7% 6% 6% 4 6% 7% 26%	3401
	21st to end	Night	19% 15% 5% 12% 8% 5% 5% 3 5% 5% 18%	5225

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	68% 4 9% 15% 4	2219
	11th to 20th	Day	61% 3 12% 19% 4	2451
	21st to end	Day	66% 5% 10% 14% 5%	3135
February	1st to 10th	Day	52% 5% 13% 21% 10% 1	1710
	11th to 20th	Day	51% 4 14% 24% 6% 1	1673
	21st to end	Day	56% 4 11% 18% 10%	1465
March	1st to 10th	Day	51% 4 12% 24% 8% 1	3377
	11th to 20th	Day	43% 3 12% 30% 11%	3480
	21st to end	Day	66% 3 11% 15% 4	3814
April	1st to 10th	Day	46% 5% 11% 23% 13% 1	2228
	11th to 20th	Day	52% 4 11% 19% 13% 1	2399
	21st to end	Day	53% 5% 11% 22% 8% 1	2470
May	1st to 10th	Day	43% 5% 12% 25% 14% 1	4148
	11th to 20th	Day	39% 4 11% 30% 13% 3	4403
	21st to end	Day	43% 5% 14% 29% 8% 1	4837
June	1st to 10th	Day	37% 5% 16% 30% 11% 1	2806
	11th to 20th	Day	43% 6% 15% 21% 14% 1	2850
	21st to end	Day	34% 6% 20% 28% 12% 1	2850
July	1st to 10th	Day	35% 8% 19% 24% 13%	4676
	11th to 20th	Day	22% 5% 18% 37% 17% 2	4648
	21st to end	Day	29% 7% 16% 33% 13% 1	4451
August	1st to 10th	Day	36% 5% 13% 32% 12% 2	4090
	11th to 20th	Day	39% 5% 14% 32% 8% 1	4080
	21st to end	Day	35% 5% 16% 31% 11% 1	4499
September	1st to 10th	Day	31% 5% 15% 36% 12% 1	2280
	11th to 20th	Day	36% 5% 18% 31% 10% 1	2132
	21st to end	Day	37% 3 13% 33% 12% 2	2076
October	1st to 10th	Day	33% 3 9% 33% 21% 1	3160
	11th to 20th	Day	38% 3 12% 23% 22% 2	3140
	21st to end	Day	47% 3 13% 27% 9%	3340
November	1st to 10th	Day	49% 5% 11% 22% 12% 2	1629
	11th to 20th	Day	59% 4 11% 17% 8% 1	1600
	21st to end	Day	55% 2 15% 20% 6% 2	1597
December	1st to 10th	Day	58% 5% 15% 15% 6%	1520
	11th to 20th	Day	59% 2 16% 18% 4	1788
	21st to end	Day	68% 3 9% 14% 6%	2442
January	1st to 10th	Night	60% 2 12% 19% 5%	4737
	11th to 20th	Night	65% 3 12% 14% 5% 1	4516
	21st to end	Night	61% 3 11% 17% 6% 1	4532
February	1st to 10th	Night	47% 4 13% 22% 12% 1	2470
	11th to 20th	Night	44% 5% 14% 23% 12% 1	2404
	21st to end	Night	48% 4 12% 21% 13% 2	2007
March	1st to 10th	Night	38% 4 15% 26% 15% 2	3479
	11th to 20th	Night	41% 4 11% 30% 14%	3480
	21st to end	Night	61% 4 8% 20% 6% 1	3817
April	1st to 10th	Night	45% 4 12% 25% 13% 1	1952
	11th to 20th	Night	50% 3 5% 24% 16% 2	1728
	21st to end	Night	48% 4 11% 22% 13% 2	1710
May	1st to 10th	Night	41% 4 10% 29% 13% 3	2819
	11th to 20th	Night	39% 4 10% 25% 18% 3	2507
	21st to end	Night	43% 4 13% 25% 12% 2	2751
June	1st to 10th	Night	32% 6% 15% 30% 14% 2	1370
	11th to 20th	Night	32% 5% 18% 26% 16% 3	1330
	21st to end	Night	27% 5% 17% 31% 17% 3	1330
July	1st to 10th	Night	35% 8% 19% 22% 15%	2185
	11th to 20th	Night	18% 4 15% 42% 18% 3	2195
	21st to end	Night	25% 7% 18% 34% 14% 3	2870
August	1st to 10th	Night	33% 4 15% 29% 15% 4	2826
	11th to 20th	Night	34% 5% 16% 33% 11% 1	2825
	21st to end	Night	29% 6% 19% 31% 13% 2	3166
September	1st to 10th	Night	26% 4 18% 34% 17% 1	1900
	11th to 20th	Night	32% 4 16% 32% 16%	2046
	21st to end	Night	33% 2 13% 34% 17% 1	2090
October	1st to 10th	Night	26% 2 7% 37% 24% 4	3795
	11th to 20th	Night	35% 3 12% 28% 20% 2	3779
	21st to end	Night	44% 3 15% 25% 13% 1	4208
November	1st to 10th	Night	43% 5% 13% 25% 12% 2	2669
	11th to 20th	Night	53% 4 13% 19% 11% 1	2800
	21st to end	Night	47% 4 17% 22% 7% 2	2799
December	1st to 10th	Night	54% 4 16% 19% 7%	2660
	11th to 20th	Night	57% 3 16% 17% 6% 1	3403
	21st to end	Night	68% 3 10% 14% 6%	5225

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	13% 14% 31% 27% 11% 3	270
	11th to 20th	Day	12% 13% 33% 33% 7% 1	270
	21st to end	Day	10% 12% 36% 24% 16% 1	297
February	1st to 10th	Day	16% 16% 36% 29% 3	270
	11th to 20th	Day	14% 16% 36% 24% 9% 1	270
	21st to end	Day	15% 12% 40% 29% 5%	225
March	1st to 10th	Day	17% 12% 40% 23% 8%	270
	11th to 20th	Day	18% 8% 36% 25% 11% 2	270
	21st to end	Day	23% 13% 26% 22% 13% 3	297
April	1st to 10th	Day	24% 14% 32% 22% 8%	408
	11th to 20th	Day	27% 15% 25% 22% 10% 1	597
	21st to end	Day	26% 10% 30% 21% 11% 2	650
May	1st to 10th	Day	20% 13% 34% 23% 9% 2	653
	11th to 20th	Day	19% 12% 28% 26% 13% 2	675
	21st to end	Day	17% 7% 33% 28% 13% 2	734
June	1st to 10th	Day	11% 7% 27% 31% 20% 4	680
	11th to 20th	Day	15% 9% 35% 28% 11% 2	680
	21st to end	Day	14% 7% 32% 27% 17% 3	680
July	1st to 10th	Day	7% 4 23% 34% 25% 7%	671
	11th to 20th	Day	7% 6% 29% 32% 19% 6%	668
	21st to end	Day	5% 4 24% 37% 23% 6%	739
August	1st to 10th	Day	9% 3 24% 34% 25% 5%	676
	11th to 20th	Day	12% 5% 22% 31% 23% 7%	665
	21st to end	Day	10% 7% 26% 31% 21% 4	729
September	1st to 10th	Day	10% 7% 31% 32% 16% 4	490
	11th to 20th	Day	12% 4 33% 32% 14% 5%	342
	21st to end	Day	18% 13% 33% 21% 13% 3	300
October	1st to 10th	Day	18% 12% 30% 26% 10% 4	300
	11th to 20th	Day	14% 17% 36% 23% 9% 1	300
	21st to end	Day	23% 14% 38% 17% 7% 1	330
November	1st to 10th	Day	24% 11% 29% 28% 6% 1	300
	11th to 20th	Day	19% 15% 42% 18% 4	300
	21st to end	Day	19% 17% 37% 24% 3	299
December	1st to 10th	Day	10% 11% 44% 26% 8% 1	270
	11th to 20th	Day	18% 14% 36% 26% 5%	270
	21st to end	Day	28% 10% 35% 21% 5%	297
January	1st to 10th	Night	11% 11% 39% 29% 9% 2	950
	11th to 20th	Night	14% 10% 38% 30% 7% 1	950
	21st to end	Night	15% 11% 39% 27% 7%	1045
February	1st to 10th	Night	10% 10% 39% 32% 8% 1	950
	11th to 20th	Night	12% 11% 43% 25% 8% 1	929
	21st to end	Night	15% 12% 33% 30% 10% 1	751
March	1st to 10th	Night	15% 9% 38% 29% 9% 1	608
	11th to 20th	Night	18% 8% 39% 29% 5% 1	570
	21st to end	Night	21% 10% 28% 28% 11% 2	627
April	1st to 10th	Night	18% 11% 35% 30% 6%	570
	11th to 20th	Night	22% 10% 32% 27% 8% 1	563
	21st to end	Night	21% 8% 32% 29% 8% 2	570
May	1st to 10th	Night	17% 10% 34% 30% 9% 1	570
	11th to 20th	Night	17% 8% 30% 33% 10% 1	561
	21st to end	Night	15% 8% 28% 37% 11%	617
June	1st to 10th	Night	12% 6% 28% 36% 16% 1	570
	11th to 20th	Night	10% 4 34% 42% 9%	570
	21st to end	Night	10% 5% 24% 47% 14% 1	570
July	1st to 10th	Night	5% 2 24% 43% 24% 2	555
	11th to 20th	Night	6% 3 28% 44% 18% 1	552
	21st to end	Night	5% 3 25% 44% 20% 3	624
August	1st to 10th	Night	8% 4 20% 46% 20% 2	567
	11th to 20th	Night	10% 4 18% 38% 26% 2	564
	21st to end	Night	8% 4 26% 37% 23% 1	627
September	1st to 10th	Night	11% 3 29% 39% 17% 2	570
	11th to 20th	Night	12% 5% 28% 35% 18% 1	570
	21st to end	Night	13% 7% 34% 32% 13% 1	570
October	1st to 10th	Night	18% 10% 32% 29% 10% 1	755
	11th to 20th	Night	19% 11% 34% 27% 8%	760
	21st to end	Night	22% 11% 33% 29% 5%	888
November	1st to 10th	Night	16% 11% 34% 32% 8%	975
	11th to 20th	Night	17% 13% 37% 24% 8% 1	1000
	21st to end	Night	15% 13% 40% 25% 7%	1000
December	1st to 10th	Night	14% 11% 36% 30% 8% 1	950
	11th to 20th	Night	19% 10% 36% 29% 5% 1	950
	21st to end	Night	24% 10% 34% 26% 6% 1	1045

Page generated at 2024-11-27 16:30:49. Version ac07

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